Remove SDK image from homepage

The SDK image isn't really needed on the home page and the flow of the
page looks better without it. Remove it and add a link to the virtualbox
page which covers the SDK.

Signed-off-by: Martyn Welch <martyn.welch@collabora.com>

content/_index.md

@@ -109,10 +109,8 @@ development, Apertis provides a number of
 (32-bit and 64-bit) for use on the Apertis
 [reference hardware]( {{< ref "/reference_hardware/_index.md" >}} ) platforms.
 
-Additionally Apertis provides an SDK image to simplify development for the
-platform.
-
-![The Apertis SD](/images/vm-sdk.png)
+Additionally Apertis provides an [SDK image]({{< ref "virtualbox.md" >}}) to
+simplify development for the platform.
 
 {{% link-box %}}
 #### Further Links